Recently, mobile phone terminals such as mobile telephones have spread rapidly. Furthermore, recent mobile phone terminals have not only simple phone functions, e-mail functions, and the like, but also various other additional functions such as multimedia (image display and audio playback) or game functions, becoming more complex every year and requiring further improvements in processing power. In addition to requirements for the improvements in processing power, there is demand for further downsizing as well as for power-saving standby time to extend battery life, and various measures are taken.
Generally, a mobile phone terminal such as those described above incorporates both MPU (Micro Processing Unit) and DSP (Digital Signal Processor), and it is common practice that among various processes performed on the mobile phone terminal, overall control is performed by the MPU while main processing part of CODEC and multimedia is handled by the DSP. Thus, that part of processing which is handled by the DSP is designed separately from the MPU, and a dedicated DSP program is created, being coded for the DSP.
During a standby time, generally, frequency of a clock supplied to the MPU and DSP is reduced to suppress power consumption.
Conventionally, mobile phone terminals mainly have phone functions. Thus, there is no problem if clock frequency is changed depending on whether the mobile phone terminal is standing by awaiting a call or engaged in a call. However, with recent mobile phone terminals, the DSP has come to handle a game or multimedia which alone causes a high load even if no call is taking place. In such a case, if the clock frequency of the DSP is kept reduced, there will be a shortage of processing power. To resolve this problem, it is conceivable for example, to add dedicated hardware or increase the clock frequency in high-load situations even if no call is taking place. However, addition of dedicated hardware will cause a cost increase and run counter to a downsizing trend. If the processing power of the DSP is increased by increasing the clock frequency, power consumption will be increased accordingly, posing a new problem: namely, the battery is drained heavily, making it impossible to stand long use without recharging.